canvas_scale_global()

The window size is defined as

• window_size = image_size * global_scale

• a = b * c

• which is equal to

• a/b = (b * c)/b

• a/b = c (simplified)

• So window_width / image_size = global scale

• Then the question becomes how to set it relative to other elements.

• (That's what the extra little number is for)

• Note that "_setting" is the automatic or user set number,

• where as with out that suffix it's the "internal" system used value.

• Context here is that it's not a "zoom".

• magic_nav_spacer is rough space between actual pane size and padding on either side of image. The goal of calculation is to make it relative to left and right panel